A tire testing machine used to measure tire uniformities (static or dynamic characteristics of a tire) includes a spindle device which rotationally holds a tire while the tire is inflated at a predetermined internal pressure, and a drum device which applies a rotational force by bringing a drum in contact with an outer peripheral surface of the tire held by the spindle device (refer to patent document 1: Japanese Patent Laid-Open No. 2004-28700, or patent document 2: Japanese Utility Model Laid-Open No. H6-45239, for example).
However, for this type of tire testing machine, it is not possible to avoid a load from being generated in the tire testing machine itself due to a tire being held in an inflated state, or being rotated while the tire uniformities are being measured, and the load causes a reduction of test accuracy.
The present invention has been devised in view of the above problem, and has an object to provide a tire testing machine, which can restrain the reduction of the test accuracy due to the load generated in the tire testing machine itself, and a method to measure the run out of the tire testing machine.
Specifically, a conventional tire testing machine includes a pair of rims used to mount a tire, a pair of spindles which support the respective rims at respective rotational centers thereof, and a lock piece which holds both the spindles so as to relatively approach to/separate from each other in a predetermined range. The pair of spindles then is disposed vertically coaxially, an upper rim is supported by an upper spindle, and a lower rim is supported at a top end thereof by a lower spindle. One of the upper and lower spindles approaches to/separates from the other one of them thereby causing the upper and lower rims respectively approach to/separate from each other relatively.
This tire testing machine loads a tire on the lower rim while the upper and lower rims are mutually separated, then causes the upper and lower rims to relatively approach to each other, thereby bringing about a hold state where the upper and lower rims are in contact with beads on the both sides of the tire, realizes an engaged state where the upper and lower spindles will not separate, and then supplies the inside of the tire with a pressurized gas (air) to inflate the tire. A drum roller is then pressed against an outer peripheral surface (tread surface) of the tire, and various measurements are carried out while the tire is rotated by a rotation of the drum roller.
However, in the conventional tire testing machine, when the tire is mounted and held, there arises an action to mutually separate the upper and lower rims caused by the state where the tire is inflated by the pressurized air (inflated state), thereby energizing the upper and lower spindles holding the upper and lower rims mutually upward and downward, resulting in eliminating a mechanical play (gap) in the engagement of the upper/lower spindles, and bringing about a stable state without a backlash. Consequently, reliable measured results are to be obtained in the various measurements of the tire. However, it is necessary to detach/attach the upper and lower rims from/to the spindles each time the size of the tire is changed, and there can be generated a variation in the positional relationship for the support between the upper and lower spindles and the respective rims. If a variation arises in the positional relationship, it always leads to an axial run out, a surface run out; and the like when the rims rotate, resulting in influence on the measured results of the tire. Moreover, if there are manufacturing errors and slight deformations caused by handling thereafter on the rims, they also cause a surface run out and an axial run out when the rims rotate.
Thus, there arises a need for measuring whether the rims are properly attached to the upper and lower spindles when the rims are respectively attached to the upper and lower spindles. The measurement of the mounted state of the rims can be optimally carried out by bringing a dial gauge in contact with bead seat surfaces (surfaces which are in contact with the beads of the tire) while the rims are rotating, and it is thus necessary to carry out the measurement before a tire is mounted.
However, in the conventional tire testing machine, since the upper and lower spindles are mutually energized upward and downward, and the upper and lower spindles enter the stable state without backlashes for the first time when the tire mounted and held is inflated by means of the pressurized air as described above, even if the state where the rims are attached is measured without a tire, there is a backlash between the upper/lower spindles, and this state cannot be used for considering a mechanical precision.
Moreover, as another factor, the spindle device of the conventional tire testing machine includes the upper spindle and the lower spindle aligned coaxially, and vertically separable. The upper spindle includes one of the pair of rims, the lower rim includes the other one of the pair of rims, both of the spindles are configured such that the upper spindle is externally engaged with the lower spindle to hold the tire between both the rims.
At an upper portion of the lower spindle is provided a through hole which passes thorough in the radial direction, and there is provided a lock piece with a circular cross section which is supported by the through hole for emerging and retracting. On the other hand, a lock portion which engages with the lock piece is provided on an inner peripheral surface of an upper portion of the upper spindle, and the vertical relative positions of the upper spindle and the lower spindle are determined by locking the lock piece and the lock portion to each other when the upper spindle is externally engaged with the lower spindle. On this uniformity testing device, the test is carried out by mounting a tire on the rims, inflating the tire with air, and rotating the tire. When the tire is inflated with air, the air pressure inside the tire generates separating forces between both the rims, resulting in a separating forces applied to the upper spindle and the lower spindle.
The separating forces are received by contact surfaces between an outer peripheral portion of the lock piece and an inner wall surface of the through hole, and the lock portion which is engaged with the lock piece.
However, in the conventional tire testing machine, since the outer peripheral portion of the lock piece is circular, and there also exists a restriction caused by the size of the lower spindle, when the separating forces are applied, the outer peripheral portion of the lock piece comes in contact with the inner wall surface along a short arc, and an actual area of the contact surfaces (receiving surfaces) of the outer peripheral portion of the lock piece and the inner wall surface of the through hole is very small, resulting in a very high surface pressure applied on the contact surfaces. If the surface pressure of the contact surfaces is very high, the outer peripheral portion of the lock piece or the inner wall surface of the through hole cannot withstand the pressure, and wear is thus generated on them, resulting in a failure.
Moreover, if a high pressure is repeatedly applied to the contact surfaces, the wear of the inner wall surface of the through hole increases the size of the through hole, a run out is generated on the lock piece when the lock piece is protruded/retracted, and the lock piece may not be locked to the lock portion properly.
Further, as another factor, the spindle device for the conventional tire test includes the upper spindle and the lower spindle which are aligned coaxially, and are vertically separable. The lower spindle is stored in a bearing housing, is rotationally supported by a spindle bearing provided between the lower spindle and the bearing housing.
Usually, when the spindles are rotated, since the spindle bearing generates heat due to rolling frictions between rollers and inner/outer rings of the spindle bearing, and the bearing housing and the spindle bearing thus expand, there is generated a difference between gaps between the rollers and the inner/outer rings of the spindle bearing before the test of a tire, and the gaps between the rollers and the inner/outer rings of the spindle bearing during the test of the tire. Therefore, when the spindle bearing is installed in the bearing housing, the gaps between the rollers and the inner/outer rings of the spindle bearing before the test of a tire are usually designed such that the gaps between the rollers and the inner/outer rings of the spindle bearing are as optimal as possible during the test in consideration of the heat generation of the spindle bearing based on the rotational speed of the tire in the test and a period of the test.
However, the amount of the generated heat of the spindle bearing during the test varies according to the rotational speed of the tire and the time, and the gaps thus change according to the temperature. Therefore, even if the gaps are set in advance such that the gaps become optimal during the test when the spindle bearing is installed, there poses such a problem that the gaps vary during the test. The variation of the gaps causes a generation of a run out of the rotating spindles, and may significantly reduce the accuracy of the measurement of the uniformities of a tire.
Further, as another factor, the spindle device of the conventional tire testing machine includes the pair of rims which are respectively brought in contact with the beads on the both side of the tire, and the pair of spindles which support the respective rims at the rotational centers thereof. In most cases, the spindles are separated vertically, the lower spindle is rotationally held by the bearing housing in a tubular shape, and the bearing housing is further held in an externally engaged state by a spindle base in a tubular shape with a larger diameter, for example.
On the bearing housing is provided a flange extending over an upper surface of the spindle base, and the bearing housing and the spindle base are fixed to each other by tightening preload bolts from the flange toward the upper surface of the spindle base in parallel with the rotational axis of the tire. On the upper surface of the spindle base are provided detectors (load detectors such as piezo elements) in a donut shape, through which the preload bolts pass, and the detectors measure loads from the tire in three directions: radial direction, axial direction, and tangential direction, through the bearing housing.
When the spindle rotates at a high speed, friction heat from the bearing, stirring heat from a lubricant, and the like are generated from the bearing in the bearing housing which supports the rotation of the spindle, and the heat influence propagates to both the detectors and the preload bolts. However, the detectors and the preload bolts are different in thermal expansion coefficient, Young's modulus, and the like, there is thus generated a difference in expanded lengths by the influence of the heat, resulting in a measurement error as a temperature drift in measured values of the detectors. Though the temperature drift can be addressed by error correction on a charge amplifier of the detectors (namely setting a state where the temperature drift occurs to an initial value “0”) for a measurement of a subsequent change, there is no means to provide a true value based on an absolute value such as a deviation of a spring force on a tire under test in response to the pressing force of the drum, which simply leads to a defect that the measurement accuracy decreases.
In the above-described conventional tire testing machine (patent document 2), though there is provided a coolant passage at a position close to the bearing in the bearing housing, and water is supplied to the coolant passage, the bearing housing is much larger in specific heat and mass compared with the coolant, the temperature of the bearing housing tends to increase as the time elapses, and the temperature of the coolant itself increases accordingly. Therefore, though there is expected a partial cooling effect around the coolant passage and a supply passage of the lubricant, there occurs a flow of heat toward the outside of the bearing housing in portions remote from the coolant passage and the lubricant supply passage, the temperature distribution consequently becomes uneven, and the temperature control applied to the detectors thus becomes difficult.
Moreover, the operation of the tire testing machine is a high speed operation or a low speed operation, or a long term operation or a short term operation, and is thus not constant, the increase of the temperature is thus not constant, and is difficult to expect, and the temperature control of the detector is thus extremely difficult.